Method of making and use of a heavy duty pavement structure

ABSTRACT

The present invention is directed to a heavy duty pavement structure comprising an open-graded asphalt layer fortified with a non-segregating grout mixture. The heavy duty pavement structure is made through the steps including forming an open-graded asphalt layer and then fortifying the layer with a non-segregating grout mixture that includes a predetermined amount of portland cement, sand and cement binder system.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 13/281,426, filed Oct. 25, 2011, which is acontinuation application of U.S. patent application Ser. No. 12/101,901,filed Apr. 11, 2008, which is a provisional conversion of U.S.Provisional Patent Application No. 60/911,492, filed Apr. 12, 2007.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to methods of making heavy duty pavementstructures. The invention further relates to the use of heavy dutypavement in high use and high traffic areas.

2. Description of the Related Art

Pavement structures designed to carry repeated heavy loads havetraditionally been formed through overlaying portland cement concrete orasphalt, to base layers of aggregate, stabilized soil or other improvednatural materials. Both concrete pavement and asphalt pavement areeffective for general use, but neither provides the necessary strengthand flexibility needed for heavy duty use.

Although concrete pavement is typically strong enough for heavy dutyuse, it is brittle and must be constructed with joints to control thecracking, and also must be constructed with a thicker cross section,thus increasing the initial cost, as well as the cost of repair.

On the other hand, asphalt pavement is more flexible under loading andhot weather, but it does not provide the strength and durabilitynecessary for the heavy duty use. In addition, asphalt pavement tends tocrack under repeated loading and cyclic cold weather and is lessresistant to abrasion and wear than concrete pavement. Since asphaltcement, the binder material in asphalt pavements, is a viscoelasticmaterial, it is soft when warm and brittle when cold. This range inbehavior, coupled with repeated truck traffic, results in the need forcontinuous maintenance of cracks, patching, and occasional overlays.

In recent years, pavement structure designs have become more complex.Multiple layers of asphalt and concrete materials, as well as othermaterials such as steel or fabric, additives or modifiers, and otherinnovations are used to reinforce and strengthen the pavement designs.

One such design combined the flexibility of asphalt and durability ofconcrete in a composite layer. In this approach, an open graded asphaltlayer was placed first, and then the open voids were filled with cementgrout. This structure known as “resin filled macadam,” does providegreater strength and durability as compared to either the asphaltpavement or concrete cement alone, but its design limitations make itimpractical for large scale use.

More specifically, the open graded asphalt layer has been constructedwith conventional asphalt cement. The use of asphalt cement limits thestrength of the asphalt component thereby making it more susceptible totemperature and loading. In addition, the grout used to fill the voidswithin the open graded asphalt structure includes ordinary (Type I)portland cement, local sand, water reducing additives (plasticizers),bonding agents (latex), and water.

Although this mixture is theoretically promising, it is impractical inuse because the freshly-mixed grout applied to the surface of the opengraded asphalt layer segregates so that the sand settles to the bottomof the open graded asphalt layer and the water rises to the top of thelayer. This results in the top part of the open graded asphalt layerhaving low strength and durability because of the relatively highwater/cement ratio. Furthermore, air voids or bubbles form within thefilled layer which displaces the grout mixture causing a lack of bondingbetween the grout and the open graded asphalt layer and the underlyingstructure layer, whether it is an existing pavement or aggregate basecourse.

In an effort to reduce the degree of grout separation, grout may bemixed in small batches and immediately applied to the open gradedasphalt layer. Although this does not eliminate the separation of thegrout components, it does reduce the degree of separation. Thisdramatically increases the time needed to complete the groutapplication. Unfortunately, rapid construction of heavy duty pavementsis necessary in order to minimize “down time” and loss of function of afacility. For high-use facilities such as ports or industrial yards thatoperate around the clock, loss of use is costly. Therefore, bettermaterials and methods are needed to make this type of heavy dutypavement more robust and economical to build, in order to realize thefull potential.

SUMMARY OF THE INVENTION

The present invention is directed to a method of making a heavy dutypavement structure. More specifically, the heavy duty pavement structurecomprises an open-graded asphalt layer fortified with a non-segregatinggrout mixture.

The heavy duty pavement structure is made through the steps includingforming an open-graded asphalt layer and then fortifying the layer witha non-segregating grout mixture that includes a predetermined amount ofportland cement, sand and cement binder system. Unlike the grout used inthe formation of the “resin filled macadam” known in the art, thenon-segregating grout of the present invention enhances the overallstrength and durability of the heavy duty pavement structure of thepresent invention

DESCRIPTION OF DRAWINGS

The invention will be better understood with reference to the figures inwhich:

FIG. 1 shows a non-segregating grout formulation for use in making theheavy duty pavement structure of the present invention.

FIG. 2 shows an alternative non-segregating grout formulation for use inmaking the heavy duty pavement structure of the present invention.

FIG. 3 shows the preferred non-segregating grout formulation for use inmaking the heavy duty pavement structure of the present invention.

FIG. 4 shows a comparison of the toughness of the present invention anda conventional low permeability asphalt layer.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a method of making a heavy dutypavement structure comprising an open-graded asphalt layer fortifiedwith a non-segregating grout mixture. The method of making the heavyduty pavement structure includes forming an open graded asphalt layerand then fortifying the open graded asphalt layer with a non-segregatinggrout mixture.

The preparation of the open graded asphalt mixture includes selection ofthe materials and is very important to achieving a quality product.There are various names typically associated with open grade asphaltmixtures, including macadam (Europe), SMA, OGFC, and the like.

The mineral aggregate, typical of that used in the highway constructionindustry must be very hard and durable, with preferably 100% crushedfaces rather than rounded gravel, but at least 75% crushed faces.Typical types of preferable mineral aggregate are crushed granite,quartzite, hard limestone, and crushed glacial or alluvial gravel. Thesizes of the aggregate particles are most preferably single-sized,meaning for example, 1-in×¾-in, or the aggregate particles capturedbetween the 1-in and ¾ in sieves when doing a screen or sieve analysis.Alternatively, the sizes might be finer, say ¾ in×½ in, but this createsa void system consisting of smaller voids that must ultimately be filledwith grout. Coarser sizes are also possible, such as 1½ in×1 in, butthis size is too large for constructing a layer that is preferably 1½ into 2 in thick. The total air voids in the compacted open gradedaggregate layer is critical to the successful filling of the voids withgrout. Ideally, the total volume of air voids in any compacted uniformsingle size material will be the same. But if the single size ofaggregate is too small, the grout may not readily flow into, and fillthe voids. The total voids in the compacted mixture may range from 20%to 35%, but preferably 25% to 30% of the total bulk volume of themixture.

The asphalt binder system used to hold the open graded aggregatetogether may be conventional asphalt material such as those calledPerformance Grade (PG) asphalts, polymer modified asphalt, asphaltenhanced with other additives such as cellulose fiber, chemicalmodification, or combinations of these treatments. Preferably, theasphalt binder system will contain MatCon Binder but may contain suchmodifiers as SBS, SBR, SB, EVA, wax, fibers, mineral filler, andcombinations of these modifiers. Although the MatCon Binder is notgraded using the PG system, the preferred viscosity and temperatureproperties may be approximated by such grades as PG 82-22, PG 76-28, andother similar grades typically used for heavy duty pavements.

The final step in the mix design process is to determine the proportionof aggregate and asphalt binder system to be used. The traditional mixdesign procedures such as Marshall Mix Design Method, Superpave DesignMethod, or similar methods used for dense graded HMA are not appropriatefor open graded paving mixtures. The basic philosophy of theproportioning design process is to include as much asphalt binder systemas possible without resulting in excessive run off or drain down. Thisrequires that as thick of a coating of asphalt binder system as possiblebe applied to the mineral aggregate in order to provide for cohesion andstrength of the final composition. In the laboratory, the process is toprepare (mix) a range of samples of hot aggregate with varying amountsof hot asphalt binder system, and place them into loose piles on saybutcher paper on the laboratory bench. The excess asphalt binder systemwill drain down and be deposited on the paper. The optimum amount ofbinder is determined by observing the amount of drained asphalt, andselecting the one with just a small amount of drain down, but notpooled. The other part of this mix design process is to determine theappropriate temperature for mixing and construction. Whereas a typicalMatCon or other dense graded HMA may require mixing temperatures in therange of 330 to 360 F, the open graded asphalt mixtures are typicallyabout 100 F lower. This lower temperature is possible because thecompaction process in the pavement is simplified because the rollingprocess is required only until the mixture is seated and smooth, ratherthan continuing the rolling process until a specified density isachieved. Depending on the nature and grade of asphalt binder systemused, the mix design process may need to be repeated using one or moretemperatures to ascertain that drain down is minimized, and thatconstruction of the final compacted pavement layer is adequate.Typically, the preferred asphalt binder system content will be in therange of 2.5 to 4.5%, and preferably about 3.5% based on the totalweight of the mixture. This design is then used at the Hot Mix AsphaltFacility to prepare the field mixtures for construction.

Example

In the laboratory, four samples of hot (275 F), pre-sized ¾ in×1 inaggregate were mixed in a blender with varying amounts of polymermodified asphalt binder system. After mixing each 10-lb batch was dumpedinto a pile on paper covered workbench, and allowed to cool to about 150F. Results are as follows:

TABLE 1 Trials to determine binder content Sample No. A B C D Asphaltbinder, % 3.0 3.5 4.0 4.5 Drain down, % 0 4 12 20

Drain down was measured as a percent of the binder on the paper comparedto the total footprint of the pile of mixture. The target was about 5%drain down, so the initial trial design was interpolated to be 3.6%asphalt binder system. The 4.5% design was intended to provide completecoverage of each aggregate particle, with a small amount of drained downbinder to serve as a tack coat on the existing pavement. The field trialbased on the first two truck loads proved that this design wasappropriate.

The open graded mixture for the composite pavement layer is prepared ina conventional hot mix asphalt plant, either batch or drum style. Themanner of proportioning the aggregate and modified binder is the same asfor conventional HMA, heating the aggregate to its maximum desiredtemperature (example 275 F) and adding the asphalt binder system at theconventional temperature for modified binders (example 360 F). Thebinder must be heated hotter in order to reduce the viscosity forpumping and mixing, and the small amount of binder (example 3.6%) willhave little effect on the overall temperature.

The existing surface to be paved may be any substrate that is part ofthe overall pavement design. These surfaces may include an existingasphalt pavement, a stabilized pavement base such as rubbelized oldconcrete or asphalt pavement, or, preferably, low permeability modifiedasphalt pavement such as MatCon, and will become part of theenvironmental cap.

The hot open graded asphalt mixture is delivered to the jobsite usingconventional dump trucks normally used for all HMA. The hot mixture istypically placed in the hopper of a paving machine normally used toplace conventional HMA. The paving machine, or paver, may be one of anyconventional design that has a static or vibrating screed, and can laydown a uniform thickness of hot asphalt mixture behind the screed. Theloose thickness of pavement will be determined by the initial rolling ofthe mixture to see how much it will compress. The end result afterrolling will be determined by the pavement design, and may range from 1in to 3 in, with 1.5 in to 2 in preferred. The upper limit of thisthickness is controlled by the ability to achieve full penetration ofthe grout to be applied. Typically, no tack coat layer of liquid asphaltis required for bonding if the open graded layer is placed on a freshand clean surface such as MatCon HMA. However, if the existing stratumto be paved is dry, open, or porous, such as a rubbelized asphaltpavement base course, a tack coat may be desirable, and can bedetermined in the field.

The desired goal of the design and construction of this open gradedpavement layer is to provide a strong and stable platform with a voidsystem to receive the cement grout. The total voids in the finalcompacted form may range in volume from 20% to 35%, but the preferredrange is 25% to 30%.

The compaction of the open graded pavement layer is achieved by a steelwheeled static roller (without vibration) and will require only modesteffort as compared to conventional dense graded HMA which may requireconsiderable compactive effort to achieve the final design density. Whenthe mixture is at the proper design temperature, it typically takes onlytwo or three passes of the roller to seat the mixture into its finalform. The final pass of the roller is to achieve uniform smoothness. Inits final compacted state, the open graded layer can carry full loadingof trucks or other construction equipment after it has cooled becausethe load is carried by the rock-to-rock resistance contact of the onesized aggregate system.

Because of the application of cement grout following paving with theopen graded asphalt mixture, it is preferable that the surface to bemaintained dry and free of dust or other detritus. Preferably, the groutshould be applied the day following construction of the open gradedlayer in order to minimize contamination. This overnight cooling periodwill then permit utilization of construction equipment on the surfacewithout danger of damage. If the construction schedule requires a fastercompletion, the grout may be applied the same day as placement of theasphalt layer, but it should be allowed to cool to at least 125 F toprevent damage such as rutting caused by equipment. It is preferablethat the open graded asphalt layer be cooled to ambient temperaturebefore applying the grout in order to minimize rapid drying and curingof the grout because the asphalt layer is too hot. The grout willachieve optimum strength and durability properties if it is cured atambient temperature while simultaneously keeping the surface wet.

The non-segregating grout formulations as shown in FIGS. 1-3 compriseseveral integrally blended raw materials. In reference to example “2”above, an economical formulation will preferably consist of a dualcement binder system, with performance additives and inert fillers. Thecement binder system is ideally a combination of hydraulically reactiveinorganic binder materials in combination with organic based coalescingbinder agents. The inorganic binder includes one or more hydraulicallyreactive materials including calcium silicate (portland cement), calciumaluminate, magnesium phosphate, or partially hydrolyzed forms of calciumoxide or calcium sulphate. Preferably, the inorganic binder will bebased on calcium silicate in the form of portland cements of type I, II,or III composition as defined by ASTM C150. Additional performancecharacteristics, as required by specific application requirements, willrequire additions to or full replacement of the calcium silicate by theother aforementioned inorganic binders.

The organic binder is based on polymers having one or more monomers fromthe group including vinyl esters, (meth)acrylates, vinyl aromatics,olefins, 1,3-dienes and vinyl halides and, if required, further monomerscopolymerizable therewith.

Suitable vinyl esters are those of carboxylic acids having 1 to 12 Catoms. Vinyl acetate, vinyl propionate, vinyl butyrate, vinyl2-ethylhexanoate, vinyl laureate, 1-methylvinyl acetate, vinyl pivalateand vinyl esters of α-branched monocarboxylic acids having 9 to 11 Catoms, for example VeoVa9® or VeoVa10® (trade names of ResolutionPerformance Products), are preferred. Vinyl acetate is particularlypreferred.

Suitable acrylate and methacrylate monomers include esters ofstraight-chain or branched alcohols having 1 to 15 carbon atoms.Preferred methacrylates or acrylates are methyl acrylate, methylmethacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate,propyl methacrylate, n-butyl acrylate, n-butyl methacrylate, tert-butylacrylate, tert-butyl methacrylate and 2-ethylhexyl acrylate. Methylacrylate, methyl methacrylate, n-butyl acrylate, tert-butyl acrylate and2-ethylhexyl acrylate are particularly preferred. Preferred vinylaromatics are styrene, methylstyrene and vinyltoluene. A preferred vinylhalide is vinyl chloride. The preferred olefins are ethylene andpropylene, and the preferred dienes are 1,3-butadiene and isoprene.

If required, 0.1 to 5% by weight, based on the total weight of thecopolymer, of auxiliary monomers may also be copolymerized. Preferably,0.5 to 2.5% by weight of auxiliary monomers is used. Examples ofauxiliary monomers are ethylenically unsaturated mono- and dicarboxylicacids, preferably acrylic acid, methacrylic acid; ethylenicallyunsaturated carboxamides and carbonitriles, preferably acrylamide andacrylonitrile; and ethylenically unsaturated sulfonic acids and theirsalts, preferably vinyl sulfonic acid and 2-acrylamido-2-methylpropanesulfonic acid. Further examples are precrosslinking co-monomers such aspolyethylenically unsaturated comonomers, for example divinyl adipate ortriallyl cyanurate, or postcrosslinking comonomers, for exampleN-methylolacrylamide (NMA), N-methylolmethacrylamide, alkyl ethers, suchas the isobutoxy ether, or esters, of N-methylolacrylamide. Comonomershaving epoxide functional groups, such as glycidyl methacrylate andglycidyl acrylate, are also suitable. Further examples are comonomershaving silicon functional groups, such as(meth)acryloyloxypropyltri(alkoxy)silanes, vinyltrialkoxysilanes andvinylmethyldialkoxysilanes.

The choice of monomers or the choice of the amounts by weight of thecomonomers is made in such a way that in general a glass transitiontemperature Tg of −50° C. to +50° C., preferably −30° C. to +40° C.,most preferably −5 to 15° C., results. The glass transition temperatureTg of the polymer can be determined in a known manner by means ofdifferential scanning calorimetry (DSC). The Tg can also be calculatedapproximately beforehand using the Fox equation. According to T. G. Fox,BULL. AM. PHYSICS SOC. 1, 3, page 123 (1956), the following isapplicable: 1/Tg=x₁/Tg₁+x₂/Tg₂+ . . . +x_(n)/Tg_(n), where x_(n) is themass fraction (% by weight/100) of the monomer n and Tg_(n) is the glasstransition temperature in Kelvin of the homopolymer of the monomer n. Tgvalues for homopolymers appear in Polymer Handbook, 2nd Edition, J.Wiley & Sons, New York (1975).

Particularly preferred are homopolymers and copolymers of vinyl estermonomers, particularly vinyl acetate. Most preferred are polyvinylacetate, copolymers of vinyl acetate and ethylene, copolymers comprisingvinyl acetate, ethylene and a vinylester(s) of α-branched monocarboxylicacids having 9 to 11 C atoms. It is possible for said polymers also tocontain, if required, one or more of the above-mentioned auxiliarymonomers.

Fillers within the system are based on silicon dioxide (also know assilica sands), calcium carbonate (also know as marble dust), or acombination thereof. Silica sand may either be naturally occurringsilica or processed, crushed silica. Particle size of the inert fillersmay range from 10 microns to 8 mm, but will preferably be in the rangeof 0.5-4 mm spread over an even distribution of particle size.Preferably, the silicon dioxide will be of a natural form, rather thancrushed with angular geometry. Calcium carbonate may encompass a similarrange, but will have a preferable particle distribution of 10 microns to1 mm.

Accelerators may consist of a family of alkili carbonate salts,polycarbonates, calcium derivatives, silicate derivatives, chloridederivatives, or aluminate derivatives. As accelerators tend to beproportionately reactive with particle size, the desired range ofparticle distribution should range from 1 to 1000 microns.

Water reducing materials include one or more materials based onpolycarboxylate ethers, melamine sulfonates, ligno sulfanates,napthalene condensates, or casein based chemistries. Preferably,polycarboxylate ethers are used due to their reactive efficiency in suchsystems.

Water retentive aids include one or more materials based on cellulose(esoterically modified or not), starch ethers, naturally occurringclays, or poly-acrylic based materials. Preferably, cellulose ether isused in the system for its inherent water retentive properties whichmaximize curing in polymer modified systems.

Defoamers include surface tension altering aids.

The purpose of the cement grout is to fill the voids in the open gradedasphalt layer, resulting in a composite pavement layer that demonstratedboth the flexibility of an asphalt pavement and the strength of portlandcement concrete. The development of a suitable grout design has beenconducted in three trials, each building upon the others to design agrout system that will be easy to construct, yet have desirable strengthand durability suitable for long time wear.

TABLE 2 Trial mix formula A Component Function Amount Source 1 PortlandCement (III) Cement 94 1bs Glacier 2 Sand (−50) Skeleton or filler 101Glacier 3 Water (potable) Hydraulic reaction 41 Tap water 4 Latex RBonding 8.8 Sika 5 Superplasticizer Flowability 0.33 Sika

The mixture shown in Table 1 and several trials using this formula weretried using a range of water content in order to achieve suitable flowproperties. An adequate mixture was achieved when the freshly mixedgrout was tested using flow as measured by 1 liter of grout flowingthrough an opening at the bottom of the vessel that measured 10 mm indiameter. A suitable mixture would flow through this device in 10 to 12seconds. The resulting water-cement ratio for this mixture was 0.44.

The goal in preparing a suitable non-segregating grout mixture is tomake it fluid and plastic in its freshly mixed wet state so that it willflow easily into the void structure of the open graded asphalt layer.After filling the voids, it should set up and cure reasonable quickly toprovide high early strength so that the pavement might be put intoservice as soon as possible. Further, the fully cured grout shouldprovide strength and durability to serve a wide range of servicerequirements such as heavy loading, abrasion due to dragging materialson the surface, and, in combination with the asphalt bound layer, shouldprovide a strong, flexible pavement structure that surpasses theproperties of either asphalt or concrete pavements alone.

Conventional portland cement concrete is made up of portland cement,sand and gravel, and water. A grout based on portland cement is made upof only cement and sand, so that the finer graded mixture can easilyenter the voids. However, a sand and cement mixture is relatively harsh,and easily segregates during mixing, hauling, and placement, i.e., thesand portion settles to the bottom, resulting in a non-uniform product.In addition, extra water may be needed to make the mixture fluid, andresults in poor quality because of the high water-cement ratio. Ingeneral, the lower the ratio between water and cement, the stronger andmore durable will be the grout or concrete. In order to overcome thisshortcoming, additives have been developed to make the freshly mixedgrout more fluid or plastic, while at the same time lowering thewater-cement ratio.

Example 1

A reasonably successful grout mixture can be formulated using thecomponents shown in Table 2. A small trial project was constructed inEverett, Wash. using the formulation shown in Table 2 and two differentmixing techniques. Using a substrate of open graded asphalt HMA, groutwas prepared by two methods: (1) batched and mixed in a large concretetransit ready mix truck, and (2) batched by hand and mixed in a mortarmixer (½ cubic yard capacity) and transported to the adjacent site usinga large wheelbarrow. All mixes met the 10 to 12 second flow requirement.It was found that the truck mixer (only partially filled to capacity)actually segregated the grout components when they were discharged ontothe pavement, and was generally unsuccessful. It is unknown if the truckmixer would work satisfactorily if it were filled with grout, since itwas not tried. The mortar mixer worked much better, producing anon-segregated grout mixture that easily filled the voids. The filledvoids were confirmed by observing 4-inch core samples cut from thepavement after one week's curing. In addition, the non-segregation ofthe grout mixture increased the overall strength and uniformity of theresulting heavy duty pavement structure.

The strength of the grout used in trial (2) was monitored by molding2-inch cube samples with the fresh grout, and curing them submerged inwater, then testing them for compressive strength at various ages ofcuring. These results are shown in Table 3.

TABLE 3 Development of compressive strength in cube samples, EverettTrial Age, days Compressive strength, psi 1 3,107 3 4,771 7 6,414 146,594 28 7,520

Example 2

Another trial was conducted in Tacoma, Wash. that also used the mixturedesign shown in Table 2. The open graded asphalt HMA pavement wasprepared in the usual way as described herein. The following day, adifferent, larger grout mixer was used that had much greater capacity(two of these mixers were utilized simultaneously). This process wassimilar to the mortar mixer, but more automated.

This machine is normally used to mix self-leveling grout for concretefloors and other structures. It has a hopper that is filled with the drycomponents (cement, sand), in ½ cubic yard batches, then mixedcontinuously with water that is metered into the mixer for each batch.The mixed grout is then pumped to the site using a continuous pump and along hose, delivering the grout more or less continuously placement. Thewet, plastic grout is spread using the hose, squeegees and brooms,followed by modest vibration using a steel drum roller compactor toshake the air bubbles from the grout and better fill the voids. Thefinished pavement was then allowed to cure for two days before being putback into service, knowing that the curing would continue as long asthere was moisture available to the grout. In the same manner as for theEverett trial, 2-inch cube sample were molded, cured under water andtested at various ages for compressive strength, as shown in Table 4.

TABLE 4 Development of compressive strength in cube samples, Tacomatrial Age, days Average compressive strength, psi 4 5,275 9 5,932 167,421

Example 3

A third trial, in Tacoma, Wash., utilized the dry mixture of grout thatis shown in FIG. 2.

The substrate was the same open graded asphalt HMA used in all trials,and varied from 1.5 to 3.0 inches thick in order to evaluate thepenetration of grout into thicker layers. The same mixing and handlingsystem used in Example 2 was used in this trial. But the addition of drymix grout (FIG. 2) was delivered in 2000 lb super sacks. The loadinghopper for the mixer was calibrated for each batch, and the appropriateamount of water was added to each batch, typically resulting in awater-cement ratio of 0.63 as originally designed.

The principal improvement of Example 3 over the preceding trials was thedelivery of the dry grout mix as a dry powder, pre-blended with allcomponents included, so all that was needed at the jobsite was to addwater. This resulted in a large saving of manpower and time, withproduction considerably faster, and better uniformity from batch tobatch. The sand component in this mixture was somewhat finer than forthe other trials, thus was more flowable and more easily penetrated thevoids. The Quality Control of this grout consistency was monitored usingboth the flow through a 10 mm orifice as well as the flow diameter on atable. For example, the diameter of the flow patty in the field testsranged from 14 to 17 cm, as compared to the designed 14 cm, indicatingthat the wet mixture had somewhat excess water. The wet grout flowed andhandled very well at the jobsite and it was easy to fill the voids withlittle effort.

It was not feasible to make cube samples for monitoring the fieldcompressive strength, but large samples of fresh grout were molded intolarge plastic pails, and de-molded after final set had occurred. Theselarger samples were kept submerged in water for 7 days, and then sent tothe laboratory where they were sawed into 2-inch cubes and tested asusual. At 28 days curing time, the compressive strength was 4,825 psi. Asecond sample, known to have excess water added (higher water-cementratio) had a compressive strength of 3,300 psi. The results of the threetrials are summarized below in Table 5

TABLE 5 Test results for various grout mixture combinations Test orProperty Blends 1-7 Blend 12 Lab batch Water cement ratio 63% 63% 63%Wet density, g/ml 2.04 2.03 2.02 Flow, Wacker method, cm Initial 14.113.0 14.2 @ 15 min. 12.2 12.1 12.2 Compressive strength, psi ASTM C 109 1 day 360 400 590  7 days 2670 3460 3440 28 days 3480 4410 4040Flexural strength, psi ASTM C 580  7 days 1970 2140 1800 28 days 21252860 2305 Linear shrinkage, % ASTM C531  7 days −0.13 −0.09 0.12 14 days−0.18 −0.17 0.15 21 days NT −.020 0.15 28 days −0.22 −0.23 0.16 Tensilestrength, psi ASTM C 307  7 days 525 425 500 28 days 542 831 540 Notes:Blends 1-7 were a composite sample of the first seven productions runs.Blend 12 was the final production run tested for single batchconsistency. The blend labeled Lab Batch is a lab blend of the rawmaterials used in production to verify homogeneity of the productionblend based on physical performance results.

The formula shown in FIG. 3 provides the optimum cost/performance ratio.However, there are variations of these that will work equally as well.All the ingredients or components shown are not required to make asuccessful grout blend. The various blends may be adjusted for localweather conditions, local need for early placement of the facility intoservice, so the mixture formulation may be adjusted without sacrifice ofquality or intended use.

The preferred water-cement ratio may range from 0.45 to 0.65 withsatisfactory results in terms of strength.

As described in the foregoing Examples, the application of grout may befield mixed and placed on the pavement in at least three differentmethods.

Methods of Application:

-   -   1 Mix in small portable mortar mixer, transport in wheelbarrow,        and place the grout where needed, followed by vibration and        squeegee to strike off flush with surface. This method is most        suitable for small or difficult to access areas.    -   2 Mix in a larger industrial mortar mixer, and pump the grout        through hoses to the pavement area, again followed by vibration        as needed and squeegee. This method may be used for larger areas        of pavement, at least ¼ acre and up to 2 acres with reasonable        productivity and resulting in a successful product.    -   3 The preferred method for large areas of several acres or more        is to use a mobile mixer that is normally used for applying        asphalt slurry seal.

It is desirable that the application of cement grout to complete theconstruction of a composite pavement be at a rate that is compatiblewith the other construction operations on the project. The constructionof open graded asphalt can be done rapidly, at a rate of about two acresper day on a large project such as an environmental cap over a hazardouswaste site. However, the previously available methods for applying thecement grout (see Examples 2 and 3) are much slower, at a rate of onlyabout ½ acre per work day. This grouting operation then becomes a severebottleneck to production. Therefore, part of this invention includes amuch improved method to apply cement grout and still maintain quality.

The first two methods were described in the Examples 2 and 3. The mobilemixer method is further described here.

The machine used to apply the grout is truck mounted and has on boardlarge bins to hold the dry grout mix. Different sized machines areavailable, but for a large project, bins that hold up to 12 cubic yardsare readily available. The dry grout mixture, for example as shown inTable 5, is shipped to the jobsite in 2000 lb super sacks, and loadedinto the truck bins using a forklift. Each super sack holdsapproximately one cubic yard of the dry powder, so as much as 12 sacksmight be used to fill one truck bin. The truck also has on board a largewater tank with a metered pump, and the appropriate amount of water canbe added. The on board mixer is a small, highly efficient pug mill typewith paddle blades, and runs continuously. The entire operation iscomputer controlled so that the proportioning of dry grout, water, andmixing is totally automated. The wet grout is discharged out the back ofthe truck as it is moving forward, and drops into a spreader box thatextrudes a uniform thickness of grout mix onto the pavement surface. Thewidth of the spreader box is typically 8 ft wide. The amount of groutbeing extruded is determined by calculating the volume of air voids inthe open graded asphalt layer. For a 2-inch thick open graded layer with30% air voids, this may be about equivalent to a layer about ¾ of aninch thick being extruded from the spreader box. A trial section istypically constructed at the beginning of each project to calibrate andconfirm the proper amount of grout to extrude. As the mixing is ongoing,the truck moves forward, spewing out the wet grout mix, and the entire12 cubic yards of grout mix is placed in about 5 to 10 minutes. A secondtruck is typically ready to continue the process while the first truckreturns to the stockpiles to reload.

In order to assure complete penetration of the grout, one or more small(1 or 2 ton) vibratory steel drum rollers follow the slurry truck tocomplete the grout installation. If the rate of application is correct,very little additional work is required, but one or two workers mayfollow the operation to smooth the surface using squeegees or brooms.Ideally, when the placement is complete, the grout is flush with thesurface of the open graded asphalt layer. Typically, there will be asmall amount of shrinkage in the grout as it cures, resulting in amodest surface texture to the finished pavement.

Because the grout is made of hydraulic cement, the surface must bemaintained wet for as long as feasible to obtain a full cure. Followingthe final set of the cement grout, it is safe to spray or flood wateronto the surface, and this may be done repeatedly, for as long asreasonable, and depending on the weather. Hot and dry weather can bedetrimental to the grout achieving its optimum strength and durability,so wet curing is crucial to success. Depending on the variation of groutblend used, the finished composite pavement may be put into service assoon as one day, preferably three days or more. For other applicationssuch as patching and pothole filling, a variation of the mixture shownin FIG. 3 can achieve strength adequate for traffic in less than onehour. This feature is very important in those situations where rapidconstruction and re-use is required for safety reasons. However, toassure proper curing, the grout strength is monitored by molding smalltest cubes of freshly mixed grout on the jobsite. These test cubes arecured in the laboratory or in the field under the same conditions asfield curing. They are tested for strength after say 1, 3, and 7 days,and the results are used to determine when the wet curing may be ceasedas well as when the pavement may be put into service.

Additional QC sampling and testing may be desirable, depending on theproject requirements or specifications. For example, core samples may becut from the composite pavement and tested for properties such asresilient modulus, compressive strength, fatigue and rutting resistance.These data can be used to confirm the design properties, and calculatesuch information as load capacity, and expected longevity.

One of the major reasons for constructing a composite pavement ofasphalt and cement grout is to strengthen the overall structure andprovide a joint-free pavement that will behave like an asphalt pavementin terms of flexibility and like a concrete pavement in terms ofhardness and abrasion resistance. As part of a project to be used forboth an environmental cap and a pavement, for example, some additionalinformation about the properties of the material are required. Theseproperties may be required for both the quality control and qualityassurance in order to prove that the final product meets allexpectations. For example, the composite pavement, in conjunction withan underlying low permeability asphalt layer (for example, MatCon), mayneed to meet the dual requirements for carrying heavy loads, while stillserving as an environmental cap. When designed and constructed properly,the composite pavement may contribute to both of these requirements.

Properties that are important for determining the stiffness or resilientmodulus, tensile strength, permeability, and toughness. In order todetermine these properties, core samples are cut from the pavements andtested in the laboratory. Results from the Example projects are includedin Table 6.

TABLE 6 Summary of pavement properties from composite pavement PropertyExample 2 Example 3 Resilient modulus, psi 1,068,000 621,750 AASHTO TP31 Indirect tensile strength, psi 315 253 AASHTO T322 Permeability,cm/sec 2.39 × 10−7 6.3 × −8 ASTM D 5084 Note: All test properties werederived from 4-inch diameter core samples, and represent the average ofseveral samples.

By comparison, typical low permeability asphalt HMA such as MatCon willhave corresponding properties as follows:

Resilient modulus 230,000 psi Indirect tensile strength 165 psiPermeability <1.0 × 10⁻⁸ cm/sec

Another material property that is important to the overall strength andperformance of a heavy duty pavement can be defined as toughness.Toughness is the area under the curve plotted from the stress-straintest. The toughness is not used in any direct computations of pavementstrength or load capacity, but can be used to compare materials in orderto judge their expected behavior under heavy loads. In order toillustrate the concept of toughness, a plot of the data from theindirect tensile strength test as shown in Table 6, for the Example 3(test result of 253 psi) is shown in FIG. 4.

FIG. 4 shows the results of plotting the stress and strain for twomaterials, composite pavement, and modified low permeability asphaltpavement. Each specimen was loaded until it failed. It is apparent thatthe area under the modified asphalt curve is much greater, andillustrates the ability to deform considerable before failure; this isconsidered plastic deformation. The composite material has a highertensile strength at failure, but does not deform as much. But when thetwo materials are compared at the same strain level, say 0.20, then thecomposite pavement will have at least 40% more area under its curve, andwill carry much more load before failure. This greater toughness in thetop layer of a pavement is a strong deterrent to deformation or rutting,and adds to the overall resistance to load. When used in combination,with the modified asphalt layer serving as an environmental cap, and thetop layer serving as a tough load carrying layer, the combination isconsiderably stronger and more durable than the modified asphalt alone.

A further attribute of the composite pavement is its relatively lowpermeability. The test values show that it is nearly as impermeable asthe modified asphalt layer used for the cap itself. When used incombination in the pavement, the overall impermeability of the structureis increased, further adding to the safety as an environmental cap.

While this invention has been described with specific embodimentsthereof, it is evident that many alternatives, modifications, andvariations will be apparent to those skilled in the art. Accordingly,the preferred embodiments of the invention as set forth herein areintended to be illustrative, not limiting. Various changes may be madewithout departing from the spirit and scope of the invention.

1. A method of making a heavy duty pavement structure comprising: a.forming an open-graded asphalt mixture layer wherein the layer includesa predetermined percentage of air voids; and, b. filling air voidsformed within the open-graded asphalt layer with a non-segregating groutmixture comprising portland cement, sand and a cement binder system. 2.The method of claim 1, wherein the open-graded asphalt mixture comprisesa mineral aggregate and an asphalt binder system.
 3. The method of claim2, wherein the open-graded asphalt mixture comprises at least 75%crushed faces of aggregate and wherein each aggregate particle is nomore than 1 inch in diameter.
 4. The method of claim 1, wherein the airvoids within the open-grade asphalt range in volume from 20% to 35%after compaction.
 5. The method of claim 1, wherein the air voids withinthe open-grade asphalt range in volume from 25% to 30% after compaction.6. The method of claim 2, wherein the open-grade asphalt mixturecomprises 2.5% to 4.5% asphalt binder system based on the total weightof the mixture.
 7. The method of claim 1, wherein the open-grade asphaltmixture comprises one sized aggregate.
 8. The method of claim 1, whereinthe cement binder system comprises a combination of inorganic bindersand organic binders.
 9. The method of claim 8, wherein the inorganicbinders comprise hydraulically reactive materials including calciumsilicate, calcium aluminate, magnesium phosphate, or partiallyhydrolyzed forms of calcium oxide, calcium sulphate and combinationsthereof.
 10. The method of claim 8, wherein the organic binders comprisepolymers having at least one monomer including vinyl esters,(meth)acrylates, vinyl aromatics, olefins, 1,3-dienes and vinyl halides.11. A method of making a heavy duty pavement structure comprising: a.preparing an open-graded asphalt mixture; b. laying the open-gradedasphalt mixture in place to form a layer; c. compacting the open-gradedasphalt layer; d. allowing the open-graded asphalt layer to cool to apredetermined temperature; e. preparing a non-segregating grout mixture;f. placing the grout mixture on top of the previously laid open-gradedlayer; and, g. filling air voids within the open-graded asphalt layerwith the grout mixture through vibratory compaction.
 12. The method ofclaim 11, wherein the grout mixture comprises portland cement, sand anda cement binder system.
 13. The method of claim 12, wherein the cementbinder system comprises a combination of inorganic binders incombination with organic binders.
 14. The method of claim 11, whereinthe open-graded asphalt mixture comprises a mineral aggregate and anasphalt binder system.
 15. The method of claim 11, wherein theopen-graded asphalt mixture comprises at least 75% crushed faces ofaggregate and wherein each aggregate particle is no more than 1 inch indiameter.
 16. The method of claim 11, wherein the air voids within theopen-grade asphalt range in volume from 20% to 35% after compaction. 17.A heavy duty pavement composite comprising: an open-graded asphaltlayer, wherein the total volume of the asphalt layer comprises between20% to 35% air voids; and, a non-segregating grout that fills the airvoids in the asphalt layer
 18. The heavy duty pavement composite ofclaim 17, wherein the non-segregating grout comprises portland cement,sand and a cement binder system.
 19. The heavy duty pavement compositeof claim 17, wherein the open-graded asphalt layer comprises at least75% crushed faces of aggregate and wherein each aggregate particle is nomore than 1 inch in diameter.
 20. The heavy duty pavement composite ofclaim 17, wherein the non-segregating grout comprises portland cement,sand, water, and a cement binder system including a combination ofinorganic binders in combination with organic binders.